Memory management in event recording systems

ABSTRACT

In vehicle event recorders which capture video as discrete image frames, a managed loop memory and management system is provided to realize a virtual ‘timeline dilation’ effect. For a buffer memory of limited size, the maximum extent of a video series in time is extended by trading a reduction in temporal resolution for an increase in temporal range. Memory cells are overwritten in an ‘interleaved’ fashion to effect a reduced frame rate for certain periods in relation to an event moment. In time periods furthest from the event moment, an effective frame rate is minimized while at time periods closest to the event moment, an effective frame rate is maximized.

BACKGROUND OF THE INVENTIONS

1. Field

The following invention disclosure is generally concerned withelectronic data storage and specifically concerned with memoryallocation and writing schemes in vehicle event recording devices.

2. Prior Art

Video recording systems are commonly used to monitor places whereactivity sometimes includes that which a record is desirable. Forexample, in a security zone criminal activity may be recorded if videomonitors are arranged about space to be monitored. When an incidentoccurs, a video record of the criminal activity is available from therecording system. During periods when no cruel activity occurs, aconsiderable amount of data is generated by the video recording system.However, this data has little or no value. Thus, it can be readilydiscarded without loss. The act of ‘discarding’ data amounts to merelyrewriting new data over old recorded data. Indeed, most video securitysystems are arranged with a recording medium that is reusedcontinuously. When a video camera generates enough image data to fullyconsume available memory, additional collected data is recorded at thebeginning of the memory. The act of writing newly acquired data is alsoan act which discards the old the data; i.e. the old data is lost to the‘write’ operation with respect to the newly collected data.

In old videotape systems, this is sometimes called a ‘round robin’arrangement. A memory medium fashioned as a tape in a continuous loopprovides the data storage for these video security systems. In suchsystems the tape has no end, and no beginning—but rather the tapecontinuously passes a recording head where new images are written to thetape at the same time old images are discarded.

When an incident of interest occurs, the tape may be stopped to preventloss of data which relates to the important incident. View images may berecovered from the tape and transferred to a permanent medium, while thetape is returned to the video system for further recording. Such re-useof memory is well known in these arts.

In a round-robin scheme, the data which is being overwritten (discarded)is the data which came into the system earliest—or was ‘first in’ thesystem. Sometimes recall the system's “first-in, firstoverwritten”—which is analogous to its close cousin, “first-in,first-out” well known from electronic buffer systems. In both cases, werefer to this method as FIFO.

A FIFO base system is generally a very good system for buffermanagement. This is due to the fact that the oldest data in a buffer istypically the least valuable. Therefore the oldest data, or the leastvaluable data, may be discarded without regard for its loss. It is notalways the case in buffer systems that the earliest received data, the‘first-in’ data, is the least valuable data in some cases is better notto overwrite the oldest data, but rather to provide an overwrite schemewhich preserves certain special portions of the oldest data.

Vehicle event recorders are video recorder systems mounted within thevehicle to provide a video record relating to the environmentsurrounding a vehicle during its operation. These systems are well knownand have been made famous for their use in conjunction with policeactivity. Many police departments in the United States are equipped withvehicle event recorders, which capture activity, sometimes criminal,which occurs in the presence of a police vehicle.

Of course, the vehicle event recorders use is not limited to policevehicles. More and more commercial vehicles are being equipped withsystems to record activity associated with the use of the vehicle andwithin the environments in which the vehicle is used. The systems areparticularly advantageous to fleet vehicles which are occasioned byheavy professional use and frequent incidents. These incidents mayinclude traffic type accidents, theft, vandalism, among others. With avideo record, vehicle fleet managers are better equipped to manage andcontrol costs associated with operations of large vehicle fleets. Safetyis improved, driver of performance is improved, confidence is gained inan understanding of accidents which do occur, and other benefits areassociated with use of vehicle recorder systems.

Some of the more advanced vehicle recorder systems are described in U.S.Pat. Nos. 6,389,340; 6,405,112; 6,449,540; and 6,718,239. Theseinventions are all presented by inventor Rayner of San Diego, Calif.Primarily these inventions relate to a small device, which is mounted tovehicle rearview mirror to capture video images of traffic incidentsahead of the vehicle.

The '112 claims in combination of vehicle which includes a vehicleoperator performance monitor. This monitor presumably records video ofthe vehicle operator, which may be used to determine how the operatorsactions affect use of the vehicle.

The '540 patent is an event recorder mounted in a vehicle which includesone or more wave pattern detectors for detection and recognition of thepresence of the predetermined wave produced external the vehicle and forproducing a trigger signal denoting predetermined wave presence. Adetective wave is of the type which is produced by a police or firedepartment emergency vehicle. Detection of this wave triggers a capturefunction which stores video images a long-term storage memory.

The '329 patent includes a one-way hash function to perform a validationfunction. In this way the integrity of the video data which is recordedcan be protected.

Finally, Rayner teaches in the '340 patent a very important relationshipbetween two different types of memory. A first memory is arranged tostore video for a short-term, and to transfer some of that stored videoin response to a trigger event. Data from this short term memory istransferred to a more durable and long-term memory. Did in the shortterm memory is continuously overwritten in a scheme which is describedby Rayner has “first-in, first-overwritten”. In this way Rayner couplesa high-speed, high-performance volatile semiconductor memory, with aflashlight memory good for long-term storage of large amounts of dataeven when power is removed. As will be described in detail later,Rayner's first in first overwritten scheme necessarily creates a loss ofimportant and valuable data.

While systems and inventions of the art are designed to achieveparticular goals and objectives, some of those being no less thanremarkable, these inventions have limitations which prevent their use innew ways now possible. Inventions of the art are not used and cannot beused to realize the advantages and objectives of the inventions taughtherefollowing.

SUMMARY OF THESE INVENTIONS

Comes now, James Plante with inventions of memory allocation schemes invehicle event recording systems including devices and methods. It is aprimary function of these systems to provide improved memory allocationand writing schemes to preserve data over extended time periods. It is acontrast to prior art methods and devices that those known systems donot record over a large time range with respect to a prescribedsize-limited memory. A fundamental difference between memory allocationof these newly presented inventions and those of the art can be foundwhen considering its time dilation, which may be applied on theextremities of discrete capture periods. The invention thus stands incontrast to methods and devices known previously.

A memory of limited size is subject to an advanced managed loop memoryallocation scheme. The storage frame rate is adjusted throughout aprescribed capture time period. At the time period extremities, a framecapture process is subject to reduced frame rate. Nearer to some instantof interest, an ‘event moment’, the frame rate is increased to improvedetail (temporal) around that particular time. The scheme permits one toaccommodate a greater temporal range at the expense of temporalresolution. Losses in temporal resolution are judiciously pushed awayfrom the event moment and allocated to the capture time periodextremities.

An overwrite scheme selects which frames are expired and subject todiscard. At any random moment, video is continuously captured at amaximum frame rate. However, these frames are not put into memory in aconventional first-in, first overwritten manner, but rather, theseframes are added to the memory locations which are determined to beavailable in accordance with the overwrite scheme. It is strictly notthe case that the oldest frame is overwritten. Quite contrarily, anoverwrite action is generally applied to a frame which is newer than atleast one other frame stored in the memory.

As a result, newly acquired frames are placed into memory in processeswhich necessarily cause older frames to be discarded. However, the newlycaptured frames are written to memory positions in an ‘interleaved’fashion whereby some of older frames are preserved. When a capture eventoccurs, data in memory may be transferred to a more permanent storage.When data is transferred, a timeline is reconstructed. The recordedtimeline is unique in that it contains various frame rates over thecapture period. At both the beginning and end of the capture period, theframe rate is modest. At the point of greatest interest in the captureperiod, the frame rate is maximum. This throttling of frame rate,permits a memory of given size to accommodate a timeline of greatertemporal extent.

OBJECTIVES OF THESE INVENTIONS

It is a primary object of these inventions to provide high-performancememory allocation systems for vehicle event recorders.

It is an object of these inventions to provide for set memoryallowances, and extended record period.

It is a further object to provide memory overwrite schemes which providea time dilation on either end of a record period.

A better understanding can be had with reference to detailed descriptionof preferred embodiments and with reference to appended drawings.Embodiments presented are particular ways to realize these inventionsand are not inclusive of all ways possible. Therefore, there may existembodiments that do not deviate from the spirit and scope of thisdisclosure as set forth by appended claims, but do not appear here asspecific examples. It will be appreciated that a great plurality ofalternative versions are possible.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

These and other features, aspects, and advantages of the presentinventions will become better understood with regard to the followingdescription, appended claims and drawings where:

FIG. 1 is a timeline illustration in proximity with a graphic toillustrate plurality of memory bin units;

FIG. 2 is a similar timeline illustration and memory graphicillustrating an overwrite operation;

FIG. 3 further illustrates the overwrite operation in conjunction with atrigger event;

FIG. 4 illustrates particular memory bins with various importanceassociated therewith;

FIG. 5 illustrates an advanced overwrite scheme to protect certain‘high-value’ video frames;

FIG. 6 further illustrates this overwrite scheme near the end of memoryspace;

FIG. 7 illustrates in detail, memory allocation with pointers to memorybins which must be saved and pointers to those bins which may be erased;

FIG. 8 illustrates four alternative versions of these inventions ofimportance which work equally well within the spirit of the overallteaching;

FIG. 9 is a block diagram illustrating important elements of theapparatus of these inventions;.

FIG. 10 is a block diagram directed to the most general methods of thesememory management systems; and

FIG. 11 is a more detailed-block diagram of these methods with greaterspecificity.

GLOSSARY OF SPECIAL TERMS

Throughout this disclosure, reference is made to some terms which may ormay not be exactly defined in popular dictionaries as they are definedhere. To provide a more precise disclosure, the following terms arepresented with a view to clarity so that the true breadth and scope maybe more readily appreciated. Although every attempt is made to beprecise and thorough, it is a necessary condition that not all meaningsassociated with each term can be completely set forth. Accordingly, eachterm is intended to also include its common meaning which may be derivedfrom general usage within the pertinent arts or by dictionary meaning.Where the presented definition is in conflict with a dictionary or artsdefinition, one must use the context of use and liberal discretion toarrive at an intended meaning. One will be well advised to error on theside of attaching broader meanings to terms used in order to fullyappreciate the depth of the teaching and to understand all the intendedvariations.

Vehicle Event Recorders

Vehicle event recorders are video image recording systems which areresponsive to triggers indicative of some event of interest.

Time Dilation

For purposes of this invention time dilation refers to an expansion of avideo sequence timeline by way of frame rate manipulation.

Trigger

A trigger is electronic means for setting some instant in timeassociated with a particular event of interest and further for causinginitiation of some associative processes.

Expanded Timeline Definition

An ‘expanded timeline definition’ is a prescribed rules set which setsforth and defines a timeline associated with a video frames sequencehaving more than one frame rate associated with any particular portionof the timeline.

Overwrite Manager

An ‘overwrite manager’ is a computer module, which determines inaccordance with an expanded timeline definition which data recorded inmemory and associated with a particular video frame is subject todiscard and may be overwritten with data from a newly collected videoframe.

PREFERRED EMBODIMENTS OF THESE INVENTIONS

In accordance with each of preferred embodiments of these inventions,there is provided apparatus for and methods of memory overwrite schemesin vehicle event recorder systems. It will be appreciated that each ofthe embodiments described include both an apparatus and method and thatthe apparatus and method of one preferred embodiment may be differentthan the apparatus and method of another embodiment.

Video event recorder systems are typically built around and deployedwith memories of limited size. This is due to the fact that, vehicleevent recorder systems may now be built very cheaply. While it ispossible to include in such devices mass storage and mass storagemanagement, for example a typical computer-type disk hard drive, thiscomponent remains quite expensive. Overall systems may be double incost, if such memories were included. Instead, a ‘lightweight’ memorysolution is embraced. An abbreviated memory or memory buffer is used totemporarily store information collected during the service day of avehicle equipped with such video event recorders. Upon return to a base,a vehicle may transfer collected information to a more permanent memoryfor management and analysis. In this way it is possible to equipvehicles with video event recorders having very inexpensive cameras andmemory.

Accordingly, memories of such video event recording systems may bepreferably handled in the following manner. A memory system is dividedinto two portions: a fast, managed loop memory buffer, and a temporarymass storage memory. Video continuously received from a video camera maybe put into the fast memory buffer. However, the amount of datagenerated by a video system is quite extensive and most of the timetotally uninteresting. However certain select portions of video capturedmay become of great interest. For example, when a vehicle is involved ina traffic accident, captured video may yield important clues as tofault, cause, identity, response, among others. In this case, it isimportant to preserve video data associated with these select videocapture periods.

To effect this, a trigger is arranged whereby the occurrence of someincident of interest, such as an automobile accident, causes data storedin the memory buffer to be transferred to a more permanent memoryfacility. Old data in the memory buffer is continuously overwritten bynew data received from the video camera in real-time. In common andsimplistic versions, this step is performed in a “first-in,first-overwritten” manner. However, there are great disadvantages todoing this. As the memory buffer is limited in its capacity to storevideo frames, “first in first overwritten” schemes provide a timeline ofcorrespondingly limited extent. For example, at a frame rate of fourframes per'second, a given memory buffer may be suitable for storing 30seconds of video frame data—or a 30 second video timeline. In ‘first-in,first overwritten’ schemes, this timeline may be arranged as 15 secondsof continuous video before a trigger event and 15 seconds of continuousvideo after a trigger event.

However it is not necessary nor advantageous to maintain a continuousframe rate throughout the entire event capture period. It is possible tohave a modest frame rate at times associated with the capture periodextremities, and a high frame rate during periods around an eventtrigger. It is for suggested here that the storage frame rate beadjusted throughout a prescribed capture time period. Such a systemallows an extended temporal range instead of a 30 second timeline, isentirely possible to have a 48 second timeline for the same memory. Sucha timeline may be embodied as 12 seconds of video at a frame rate of oneframe per second for the periods of time furthest from the eventtrigger, both before and after. In addition, the video sequence mayinclude video for 24 continuous seconds, 12 seconds before and 12seconds after an event trigger, at a video frame rate of four frames persecond. In this way, the temporal range is extended but the temporalresolution is compromised in the time periods furthest from the triggerevent.

To bring about this managed loop memory buffer management system, anoverwrite scheme is provided to select which frames are ‘expired’ and nolonger part of the particular extended timeline scheme. What is remindedthat video is continuously captured at all times; and further this videois captured at the maximum frame rate. This is necessary because it isnot possible to know whether or not an event trigger will be coming inthe next instant. Accordingly, the system always captures video at themaximum frame rate as the capture frame rate cannot be adjusted in viewof any event trigger which may come in the future. Video captured at themaximum frame rate is put into the memory and as it is put in the memoryit displaces previously recorded video frames. These frames are added tothe memory locations determined to be available in accordance with aprescribed overwrite scheme such as the one mentioned. However, thisstep is provided in striking contrast to a first in first overwrittenscheme. In these novel systems, most frames being overwritten areactually newer than at least one other frame stored somewhere in thememory buffer. Newly captured frames are written to memory positions ina pseudo—‘interleaved’ fashion where some of olderframes are preserved.

When a trigger event occurs, data in memory is transferred from thememory buffer to a memory of more permanent nature. When this data istransferred, an expanded timeline is reconstructed as a timeline havingat least two frame rates. At the extremities of the capture periodtimeline, the frame rate is reduced. At and about the point of greatestinterest (trigger event) in the capture period the frame rate ismaximized. This ‘throttling’ of frame rate, permits a memory of presetsize to accommodate a timeline of greater temporal extent; albeit withreduced resolution in some places.

A better understanding of these inventions may be had with reference todrawing FIGS. 1 through 11 and the reference numerals set forth therein.In particular, FIG. 1 illustrates a simple example timeline associatedwith a memory system which has been divided into a plurality of memorybins. To develop the example, some arbitrary numbers for memory size,number of bins, video frame rates, et cetera, are selected. It is to beunderstood that these are not necessarily preferred values, but ratherthey are sensible and realistic values which promote a more clearunderstanding of the illustrative example.

The memory in question, the high-speed, high-performance memory, oflimited extent. This memory is arranged as a buffer. It is put intocommunication with incoming video data recorded by a video camera. It'soutput, is directed to another data storage means, but one perhaps amemory system having far greater capacity but less speed. A memorysuitable for use in this fashion includes in example a semiconductorDRAM type memory. Alternatively a non-volatile high-performance memoryfor example those arranged about ferromagnetic principles. This memoryis primarily characterized in that it is quite fast and responds inreal-time to video collected by a video camera, however it is of limitedsize and not suitable for saving the mass amounts of data generated byvideo image systems.

We can say for purposes of a useful example that this memory size islimited to the few megabytes. The memory is arranged to temporarily holda limited number of video frames which may or may not be transferred toa more permanent memory in a transfer operation. It is convenient anduseful for a clear illustration to say that the memory is divided into120 bins; each been be sufficient for storing the data associated with asingle video frame.

We also associated timeline 1 with this memory. This timeline iscomprised of a 30 second time interval. The timeline is marked in theFigure from 0 to 30. A one second interval 2 is illustrated at thebeginning of the timeline. Further, that one second interval is dividedinto quadrants, representing a quarter of a second interval 3. For thevideo systems of immediate interest, this quarter of a second intervalnicely accommodates a single video frame (implicitly setting a framerate of four frames per second). While most modern video systems havefar higher performance than recording four frames per second, fourframes per second is a useful rate for vehicle recorder systems whichtend to have limited memories in the interest of maintaining low-cost.Further, the kinds of events being recorded in vehicle recorder systemsare well served by frame rates of a few frames per second.

When video images are captured by a camera, frame-by-frame, each frameimages can be recorded into a memory bin 4. A first frame is recordedand put into a first memory bin. Thereafter, a quarter second later, asecond frame is recorded and put into an another memory bin—perhaps anadjacent bin. This frame-by-frame recording scheme may continue for upto 30 seconds before all memory bins becomes full and the supply ofempty bins is exhausted. In the figure, the first 116 memory bins areshaded to indicate that one frame each of video data has been written tothose bins. This is equivalent to recording of a video signal 5 of fourframes per second for 29 seconds. The Figure illustrates four emptymemory bins 6, which would be filled in the next second of videorecording. Recording video images in this manner, is well-known andcommonly found in the arts; as such, the Figure is labeled (prior art).

FIG. 2 illustrates a similar timeline 21 in conjunction with a graphicalillustration of a memory having 120 memory bins. As presented in FIG. 1,a time interval equivalent to one second 22 as well as a time intervalof one quarter second 23 is illustrated for reference. The graphicaldepiction of the memory includes lightly shaded areas 24 and 25. Thememory bins presented as 24 represent those bins having data writtenthereto from video which was collected from a time t=14 up to a timet=30. The demarcation indicated as dotted line 26 reminds us where timet=14 is. At time t=30, the memory is completely full. Video datacollected for 30 seconds at four frames per second fills 120 memorybins. The video data collected at time t=31 cannot be saved to memoryunless a portion of the memory already allocated and consumed in aprevious data write step is overwritten. Thus in the graphic, we presentmemory bins indicated by 25 on a second line to represent that videoframe data is recorded in these memory bins at the expense of datacaptured 30 seconds prior. Accordingly, for the time period indicated,i.e. video data collected from t=0 to t=14, the data is lost to anoverwrite step. In the figure, those bins shaded dark are indicated as27, represent the ‘over written bins. This effectively illustrates theso-called ‘round-robin’ or ‘first-in, first-overwritten’ FIFO memorymanagement schemes. Since these schemes are very well-known, this figureis also labeled (prior art). The FIFO memory management scheme is veryuseful. When a new video frame is collected by the video camera it isplaced into memory at the same location as the oldest frame in thememory which is discarded in the overwrite step. The FIFO memorymanagement scheme implies the oldest video information in the memory isthe least valuable.

The memory described is a buffer memory. That is, this memorytemporarily holds the data of a video series for some specified time,but also continuously discards previously recorded information. When thebuffer contains a data set associated with an important event, that datais transferred from the buffer memory to a more permanent memory beforebecoming subject to lost by overwrite actions. A video series becomes‘important’ when a detectable event occurs which implicitly indicatesvideo is valuable. For example, if a vehicle is involved in a trafficaccident, accelerometers can detect the accident and trigger a transferof data from the buffer memory to a permanent memory.

In those vehicle event recorder systems, a trigger is sometimes arrangedto indicate that such an event has occurred; an event for which thevideo images associated therewith may be of extreme importance. In thiscase, the short term buffer memory of 120 video frames, should betransferred to a more permanent long-term memory for example, a durableflash type memory.

FIG. 3 is directed to illustrate a timeline which includes an eventmoment. FIG. 3 includes a timeline 31, and the dashed line 32 toindicate the 29th second along with a marker ‘X’ 33 to indicate atrigger event has occurred at the 29th second. When a trigger eventoccurs, it is important to preserve the video data which occurred afterthe accident as well as the video data which occurred before theaccident. Video images collected during a time period starting 15seconds before the accident are in the bins indicated by 34; i.e. thosevideo image frames collected between t=14 and t=29. Memory bins at theend of the time line indicated by 35 include four video frames collectedduring the first second after the accident. Video image frames collectedbetween t=30 and t=44 are placed in the memory bins indicated by 36.Thus the memory buffer contains video images for 15 seconds prior to theaccident and 15 seconds after the accident; the memory of limited sizecan only hold video image data which represents 30 seconds of videorecording.

At this point in time, no new frames are recorded to memory; overwriteis prevented, and the memory buffer is “locked”. Rather, the systempauses to transfer data in the buffer memory to a permanent flashmemory. After data is successfully transferred to flash, the buffer is“unlocked” and may be used again in the fashion described. It is usefulto note that as video data which was placed into buffer memory binsbetween time t=30 and time t=44, it caused older data to be displaced,overwrote and forever destroyed. Data which was recorded between t=0 andt=14 is completely lost and we have no access whatever to thisinformation which at one time resided in those memory bins—thatinformation was destroyed in the overwrite step. It is first suggestedhere that some of this information may be very valuable and it is quiteundesirable to lose it entirely. Indeed, it is suggested that some ofthis data is more important than data which is being saved in its place.

Since the moments which led up to a vehicle accident sometimes canexplain a great deal about the complete story, it is highly desirable tohave at least have some limited information relating to the scene at t=1for example. If we can just see one frame at t=1, it may prove to beextremely valuable in explaining what happened in the accident. Thus onecan argue, that the oldest frame in the memory at a time t=30; onesecond after the accident, is not in fact the ‘least’ valuable frame inthe memory. In this case at t=31, the FIFO scheme may be actuallydestroying critically useful data.

This is more readily understood, in consideration of FIG. 4 whichexplicitly shows certain bins A-F associated with various points of thetimeline 41 and with reference to trigger event 42 time at time t=29.The following discussion further illustrates the importance of thosebins A-F.

In a FIFO system, all memory bins, indicated by 44 and 45 are preservedin the memory buffer. Amongst the oldest recorded video frames remainingare those which lie in memory bins A and B. These represent two adjacentframes; frames which are captured within a quarter of a second from eachother. Since these frames represent images very close in time, theseframes are expected to be quite similar to each other. While it issometimes desirable in video systems to have high temporal resolution,i.e. as many frames per second as possible, one will appreciate that athigher frame rates, adjacent frames will contain much the sameinformation as those closest thereto. Accordingly, where memory islimited these adjacent frames loose their importance as most of theinformation contained in each frame is similarly contained in theadjacent frame. Thus, if we keep frame A and discard frame B, most ofthe information of frame B can be known by examining frame A.

On the other hand, frames D, E and F, which are discarded in a FIFOsystem, may actually contain extremely important information. Frame D isseparated from frame E in time by one second. In a video scene, theremay be considerable differences between one frame captured an entiresecond later than another frame. Further, frame D occurs a full 29seconds before the trigger event. In a traffic accident, it can be quiteuseful to know about what was happening a time periods further, bothbefore and after, from a trigger moment. Thus it may be possible in amemory having a finite number of memory bins to trade some of the binsassociated with less important time slots for bins associated with timeslots having a greater importance. If we discard frame B, and preserveframe D, we may gain a greater overall understanding of the incidentbeing recorded. In effect, we can trade some time resolution (framerate) at t=15, for improved overall temporal range to realize anextended timeline.

The careful observer will notice if we preserve video data associatedwith a frame rate of one frame per second, in seconds 1-12, then we willstill have available to us 36 memory bins into which will accommodatenewly captured video data. Thus, rather than completely overriding theoldest video data in memory, one can perform an overwrite action on 3 ofevery 4 memory bins in the overwrite portion of the timeline, therebymaintaining ¼^(th) of the oldest video data in those memory bins. Thatis to say, for the oldest video data in memory it may be useful to saveone frame per second. To effect this, when the overwrite operation isexecuted, new data is written to three memory bins, before one bin isskipped. This is repeated.

Timeline 51, includes a trigger event 52 at time t=29. In a particularoverwrite scheme of interest, it is prescribed that a timeline becomprised of 12 seconds of low temporal resolution, 24 seconds fulltemporal resolution and a further 12 seconds of low temporal resolution.This is further defined in detail as: a 12 second period of one frameper second video, a 24 second period of four frames per second video,and finally a 12 second period of one frame per second; for a totalvideo sequence of 48 seconds. Since it cannot be known at what time inthe future an event trigger will occur, a data overwrite scheme mustpreserve data associated with various frames from which a prescribedtimeline is comprised. In the example being developed here, continuousvideo data at a frame rate of four frames per second is preserved for aperiod of 12 seconds 54 before the trigger event; that data is in memorybins indicated by 53. It is acknowledged that in the FIFO system one canpreserve data at four frames per second for up to 15 seconds before andafter the trigger event. The newly proposed system, it is suggested thatonly 12 seconds of four frames per second data be kept. However, it willbe shown for this small price, we can dilate the total timeline of thevideo sequence to 48 seconds in contrast to the 30 second timeline ofthe FIFO system.

In the 31st second, the first overwrite operation begins. Whether or nota trigger has occurred, newly captured video data is written to everythree out of four memory bins leading the fourth memory beenundisturbed. That is to say old data is preserved, albeit at one quarterof the frame rate, from which it was originally recorded. Video dataafter the trigger event is recorded in the memory bins 55 a frame rateof four frames per second. Just because some bins are skipped, it is notnecessary reduced the frame rate of video data collected after thetrigger event. This is readily understood in consideration of the timepoint indicated by 57 which indicates the time t=41 seconds. Withoutskipping bins, this point in memory would be time t=45. Carefulobservation will prove that the bins indicated by 55 will accommodatedata at four frames per second for the entire 12 seconds after the eventtrigger. After time point indicated by 57, there remains several memorybins available for further overwrite operation before reaching thememory bins which contain data which must be preserved in agreement withthe timeline definition 12/24/12. At least some of those memory bins upto the position indicated by 54 are available for overwrite. After thefull 12 seconds of four frames per second video is recorded, it isdesirable to continue recording video data at one frame per second oradditional 12 seconds. Data captured in this period can be stored inmemory bins, which are scattered in various locations about the memorybuffer. FIG. 6 will help illustrate where these positions lie.

FIG. 6 illustrates memory bin locations which are available foroverwrite as the memory approaches its full capacity for the particularschemes presented here. Once a trigger event occurs, i.e. is set intime, it is possible to compute which video frames must be saved inaccordance with the particular timeline definition, and which ones aresuitable for discard. To further our illustration, we suggest that 48frames at four frames per second are preserved immediately before thetrigger event. In addition, 12 frames at a video rate of one frame persecond are preserved for the time t=5 up to t=17. These frames must beprotected from any further overwrite operation. i.e. these frames aremarked “must be saved” in the figure. These frames are saved as they areincluded in the timeline definition. All frames which precede t=5 are incondition for discard. That is, they lie outside the time range which isto be preserved. Accordingly, frames indicated as 69 for example haveaged sufficiently and are okay to erase. These are frames whichoriginally were preserved in the overwrite operation as skipped frames.

Video frames captured after the trigger event are also saved in thememory. For 12 seconds after the trigger event, t=29 to t=41, video iscaptured at a rate of four frames per second. That video data 65 is putinto memory in accordance with the need to save particular frames of theoldest video data. When all video frames from the period t=29 to t=41are properly recorded, the system continues to record data a frame rateof one frame per second. This is distinct, from the earlier operationwhere the overwrite action resulted in preservation of one frame persecond. For the time period 12 seconds after the event trigger up to 24seconds after the event trigger, data is put into memory at a reducedframe rate of one frame per second. Other frames may be captured by thecamera, but they are discarded before entering the memory or instantlythereupon. Thus frames represented by 67 are put into memory bins whichare available in accordance with the “OK to erase” label in the drawing.A careful observer will note that after three of these frames are placedin the memory, the fourth frame 68 cannot be placed into the memory inthe same repeating geometric position. That is to say, those memory binsare not available for overwrite. As such video captured after that time,must be carefully managed and fit into memory bins which are available.

FIG. 7 illustrates the steps taken in the final filling of the remainingmemory bins. The reader will be reminded of the timeline 71 and theevent trigger 72 at time t=29. In agreement with the example timelinedefinition, video captured at a frame rate of four frames per secondfrom t=17 to t=29 is stored in memory, as indicated by 73. Similarly,video captured for a 12 second period at a frame rate of four frames persecond from t=29 to t=41, is stored in memory as shown 74. Finally,video frames captured during a 12 second period from t=42 to t=54 at aframe rate of one frame per second include those particular framesrepresented as 75. Those frames must be inserted into the memory binswhich remain available for overwrite. Arrows 76 indicate that theseframes may be placed in locations near the memory beginning where datahad once been stored but is now expired due to the fact that the triggerevent occurs at t=29. Once a trigger event is established, the binswhich may be overwritten is determinable in an agreement with theparticular rules which define the timeline.

The specific example presented clearly illustrates that carefulmanagement of an overwrite scheme permits a memory buffer to dilate atimeline by manipulation of which video frames are preserved and whichare overwritten. In effect, temporal resolution is sacrificed to extendtemporal range. That is to say, the frame rate of “saved data” isaltered in order to make more space for video frames captured further intime from the event trigger. In this way, the greatest amount ofinformation can be preserved in a memory buffer of the limited size.While the example illustrates in exhaustive detail where data is writtenin memory for illustrative purposes, experts will note there is reallynothing sacred about the physical positions of memory bins. Therefore,it is explicitly set forth here that after a timeline definition is set,it is a simple matter to prepare an algorithm which defines at any timethe bins which contain data that has expired and thus implicitly definesa bin available for overwrite.

While the specific example presented in FIGS. 5-7 nicely illustrates oneelegant solution, it should be well understood that many very usefularrangements will permit a time dilation in accordance with the spiritof these inventions. Particular values used may be different than thosepresented in the example timeline definition. In another exampletimeline definition, one might arrange a system whereby two periods ofeight seconds are used to capture video of high frame rate, and twoperiods of 28 seconds are used to capture data at a low frame rate—thusachieving a total expanded timeline of 72 seconds. The usefulness ofthese inventions does not depend upon the particular values chosen inthese examples. Further, one should recognize that sincecapturing/saving video at two different frame rates allows one to expandthe timeline, that similarly capturing/saving video at three differentframe rates also allows one to expand the timeline with moreflexibility. That is, it is possible to manage the memory such that forsome time periods frames are preserved at a rate of four frames persecond, in other time periods, frames are preserved at a rate of twoframes per second, and still further in other time periods frames arepreserved at a rate of one frame per second. In this way, we canmaintain very high temporal resolution for the periods immediatelysurrounding an accident (trigger event), to have a medium levelresolution for periods further away from the trigger event, and finallyat the furthest extremities of the time range we can have very lowtemporal resolution. Such extensions should not be considered newinvention, but rather a subset of inventions first taught in thisdisclosure.

In addition, we explicitly anticipate asymmetric timeline definitions.That is, the time periods on either side of the event trigger may not beequal in extent or number. It is possible to devise a timelinedefinition having a long, high resolution period before the eventtrigger and a short high resolution period after the event trigger. Toillustrate various timeline definitions of interest, the FIG. 8 has beenprepared with several examples each working equally well within thecommon concept of timeline dilation. FIG. 8 graphically illustrates afirst memory buffer 81 example presented in detail above. In thisexample, there are two frame rates, a high video frame rate of fourframes per second and a low video frame rate of one frame per second. Atrigger event 82 which occurs at some instant in time implicitly setsthe time periods for any particular example. In the example presented,time periods 83 starts immediately after the trigger event and extendsfor 12 seconds. A second time period 84 extends from the trigger eventto 12 seconds prior to the trigger event. In both of these time periods,video captured and put into the memory buffer at a rate of four framesper second. The number of shaded memory bins reflect a frame rate of 4frames per second. Time periods at the extremities of the timeline,periods 85 and 86, are each also configured to be 12 seconds in length.However, since only one frame per second is collected in those timeperiods, the number of memory bins consumed is considerably smaller;i.e. ¼ those consumed in the other time periods. This arrangementprovides a total timeline of 48 seconds. In memory buffers which do notoverwrite/store data at variable rates, the same memory size would onlybe able to accommodate a timeline of 30 seconds. FIFO memories of thesame size are restricted to 30 seconds.

Example 2 presented as 87 in the drawing figure, suggests two hightemporal resolution periods of 10 seconds each. In addition, there aretwo low temporal resolution periods each of 20 seconds. While there is areduced overall period of high-resolution video data, the total timelineis extended to 60 seconds.

Example 3 is presented in the memory buffer of graphic 88. Thisimportant example illustrates that is possible to configure anasymmetric timeline definition. It is not necessary that the two periodsin which high video rate recording occurs are the same in extent. Indeedit is possible to record video at a high frame rate for a longer periodafter a trigger event than that period immediately before the triggerevent. In this example, video is recorded in the memory buffer for 16seconds after the trigger event, but only for four seconds prior to thetrigger event. In this way, the total high-resolution time period is thesame as the example above, 20 seconds, but greatly favors preservinginformation after the trigger event, at the expense of information priorto the trigger event.

In a final example, there are six distinct time periods from which thetimeline is comprised. Two 9 second periods occur symmetrically about anevent trigger. In these time periods video may be captured a rate offour frames per second. Two additional periods each of eight seconds maybe used record/overwrite data at a frame rate of two frames per second.In two additional 8 second periods are provided to store data at a framerate of one frame per second. The reader will note that in the timelineof this example, two of the 8 second periods are of different sizes withrespect to memory capacity, i.e. greater number of bins, than the othertwo 8 second periods. This is consistent with the higher frame rate usedin two of the eight second periods.

It is now very easy to appreciate the great latitude one has whenmanaging a memory buffer of limited capacity to expand a timeline. Onefurther appreciates that where memory buffers deploy FIFO or‘round-robin’ strategies for overwrite operations, very important datamay be lost. FIFO and ‘round-robin’ strategies discriminate against theoldest data in a memory buffer. In cases where the oldest data is notthe least valuable, FIFO and round-robin strategies are inferior.

With attention directed to FIG. 9, one will appreciate more clearlyfundamental elements of apparatus of these inventions. These systems arealways comprised of a video camera 91 operable for collecting opticalenergy and converting into an electrical signal which represents theimage of a scene. The camera produces an electrical signal, suitable forprocessing by common electronic means such as digital semiconductormemories and processors. In addition, these systems include a triggermechanism 92. In preferred versions, a trigger mechanism is the devicearranged to provide an electrical signal to indicate that a particularvideo series should be transferred to permanent memory for long-termstorage. A trigger may be an accelerometer operable for detecting abruptchanges in speed, for example that which may accompany a trafficaccident. A trigger may be activated by other events such as heavybraking or swerving maneuvers. Triggers may be activated by means otherthan accelerometers. For example, a user panic button can be used toactivate a trigger event. When the user comes to his own conclusion thata video series should be saved, he can hit a panic button to activateone type of trigger. It is not of particular concern for purposes ofthese inventions what precisely causes a trigger to be activated, butrather the response in memory handling once a trigger event hasoccurred. An overwrite manager 93 is a control module which interfaceswith the trigger and a video camera, and also a buffer memory 94. Anoverwrite manager includes means where a timeline definition may be setand further means for executing overwrite operations in agreement withthe stored timeline definitions. Further an overwrite manager mayadditionally integrate with a flush module 95. When a trigger eventoccurs, the overwrite manager continues to overwrite data to the buffermemory in accordance with the timeline definition by way of an overwritepointer which is associated with a cell subject to an impendingoverwrite action. The overwrite manager sends a signal 96 to the flushmodule 95 to cause the flush module to copy the buffer memory andtransfer the video data set with the prescribed expanded timeline to ahigh-capacity long-term storage 97. It is the overwrite manager whichcontrols the algorithms and necessary processing facility which decideshow to write to the buffer memory in order that select data is saved andredundant data is purged in accordance with a particular expandedtimeline definition.

Preferred methods of these inventions are more easily understood in viewof the block diagrams of FIGS. 10 and 11 which illustrate the primarysteps of these methods. In particular, FIG. 10 suggests the most generalmethods which contains two steps including: a step 101 whereby framedata is received from a video camera, and second a step 102 whereby thatnewly received data is written over old data stored in the memory bufferin agreement with an expanded timeline definition.

FIG. 11 illustrates these methods in greater detail. Frame data isreceived 111 from a video camera and a first step. The buffer memorydata write step 113 includes three distinct processes including: a step114 where the frame is written to of been marked open. It is importantpart of this invention that data be written in the buffer memory in anorganized fashion. So as not to disturb particular data frames, whichare necessary to fill the prescribed expanded timeline definition.Therefore, a bin is marked ‘open’ when it no longer contains frame datanecessary for the expanded timeline definition. In a second sub-step115, a determination is made with regard to which memory been containsframe data, which is no longer needed in agreement with the timelinedefinition. This determination must be taken up on each cycle. For everynew frame which enters the buffer memory another frame becomes no longernecessary at the same instant. Finally, in the third step, the bin whichcontained the no longer needed data is marked ‘open’. In the followingcycle 112, the next incoming frame is written to the appropriate bin. Itis useful to set a buffer memory pointer in agreement with thisdetermination to effect a bin being marked ‘open’.

One will now fully appreciate how advanced memory management schemes maybe deployed to expand a recorded timeline in memory buffers havinglimited capacity. Although the present inventions have been described inconsiderable detail with clear and concise language and with referenceto certain preferred versions thereof including best modes anticipatedby the inventors, other versions are possible. Therefore, the spirit andscope of the invention should not be limited by the description of thepreferred versions contained therein, but rather by the claims appendedhereto.

1) Vehicle event recorders comprising. a camera; a managed loop buffermemory; and an overwrite mechanism, said camera is operable forconverting optical images to electronic signals suitable for recordingin said managed loop buffer memory, said managed loop buffer memory is arandom access, re-writ able, electronic storage medium of finite sizesuitable for storing data, and in particular data arranged as discretevideo frame data, said overwrite mechanism electronically coupled tosaid managed loop buffer memory and arranged to manage data overwriteoperations whereby a first video frame older than a second video frameis saved in the memory while the second frame is overwritten. 2) Vehicleevent recorders of claim 1, said overwrite mechanism being arranged tooverwrite data associated with a frame not the oldest frame in memory.3) Vehicle event recorders of claim 1, said overwrite mechanism beingarranged to overwrite data in an interleaved fashion whereby aneffective frame rate is preserved by performing overwrite operations onalternate frames or frame sets. 4) Vehicle event recorders of claim 1,said overwrite mechanism further is comprised of an overwrite pointerarranged to point to a cell to be overwritten in a future overwriteaction. 5) Vehicle event recorders of claim 1, said overwrite mechanismfurther comprising a timeline definition which defines an expandedtimeline and virtual frame rates and periods for those frame rates. 6)Vehicle event recorders of claim 5, said timeline definition includesone having three distinct periods and an event moment at the timelinemidpoint whereby the frame rates associated with the periods at thetimeline extremities is lower than the frame rate associated with theperiod including the event moment. 7) Vehicle event recorders of claim5, said timeline definition includes one having five distinct periodsand an event moment at the timeline midpoint whereby the frame ratesassociated with the periods at the timeline extremities is lowest, andthe frame rate associated with the period including the event moment isthe highest. 8) Vehicle event recorders of claim 5, said timelinedefinition includes an asymmetry whereby the frame rate is different forthe periods after an event moment than the periods before an eventmoment. 9) Vehicle event recorders of claim 1, further comprising asecond memory, a high capacity, long-term memory coupled to the managedloop buffer memory. 10) Vehicle event recorders of claim 9, furthercomprising an event trigger arranged to cause a transfer of data fromsaid managed loop buffer memory and said high capacity long-term memoryin an expanded timeline format. 11) Vehicle event recorders of claim 9,said transfer of data step resets the managed loop memory into aninitial state and a new timeline is initiated. 12) Vehicle eventrecorders of claim 9, data in long term memory is not overwritten insuccessive data transfer steps as it includes capacity sufficient for aplurality of events. 13) Methods of dilating a timeline of a videoseries in a vehicle event recorder video managed loop buffer memorycomprising the steps: receiving electronic signal data associated withvideo frames from a video camera; and overwriting previously writtendata with newly received data, whereby previously written data iscomprised of that belonging to a frame which is not the oldest frame inmemory. 14) Methods of dilating a timeline of claim 13, said overwritingpreviously written data step includes overwriting data in an interleavedfashion whereby successive frames are skipped with reference to theircapture times to effect an effective reduced frame rate. 15) Methods ofdilating a timeline of claim 14, further comprising the step of movingan overwrite pointer to a cell not a member of a timeline definition.16) Methods of dilating a timeline of claim 15, further comprisingapplying an overwrite operation to the cell associated with the pointerand further moving the pointer to another cell not part of the timelinedefinition. 17) In a vehicle event recorder system, a managed loopmemory comprising: a coupling to a video camera output whereby imagesfrom the camera are received at said managed loop memory; a plurality ofmemory cells each being associated with a single video frame; anoverwrite pointer associated with precisely one memory cell; and atimeline definition, whereby said timeline definition directs theoverwrite pointer to be associated with a cell which no longer remains amember of the timeline definition thus subjecting that cell to animpending overwrite action. 18) Managed loop memory of claim 17, saidtimeline definition comprising two 24 second periods of 1 frame persecond and one 48 second period of 4 frames per second, either of said12 second periods falling before and after the 48 second period.